Fluidic cell guidance for flow cytometry

ABSTRACT

The invention relates to a device and a method for fluidic cell guidance for flow cytometry or analyte enrichment. This allows magnetically marked analytes, in particular cells ( 1 ), to be dynamically enriched and individually detected in the flow from a sample, in particular magnetoresistively. For cell guidance, guiding ridges ( 12 ) are arranged in a flow channel ( 100 ), and so, in addition to a magnetic enrichment force ( 10 ) and the shearing force of the flow ( 10 ), a deflecting force ( 10 ) caused by the fluidic obstacles ( 12 ) also acts on the cells ( 1 ) to be detected.

The present invention relates to flow cytometry, and in particular to cell guidance.

In the field of cell measurement and cell detection, optical measurement methods, such as scattered-light or fluorescence measurement, and magnetic detection methods are known.

Particularly in magnetic detection methods, for cell sorting, cell guidance or cell enrichment, magnetophoresis is known, in which a magnetic force is exerted on the marked cells by means of magnetic guide strips, in such a way that these cells can be separated or also aligned with a cell measuring device following these guide strips. To date, with the aid of a gradient magnetic field, enrichment of marked cells or particles has been carried out on a substrate surface on which the cells, or particles to be detected, are in turn aligned by means of magnetophoresis.

In order to produce such a magnetophoretic enrichment and alignment section, it is known to apply magnetic strips onto the substrate, for example by lithography. Such production methods, however, are very elaborate and therefore disadvantageous for the production of a component which is intended for large production numbers owing to its use. A further disadvantage of the magnetophoretic enrichment section is the silicon footprint thereby increased. For the integration of an enrichment section and cell measuring device on a silicon chip, the size of the latter exceeds reasonable costs for the use of such components.

It is an object of the present invention to provide a more simply producible apparatus for flow cytometry.

The object is achieved by an apparatus as claimed in patent claim 1. A method for cell guidance is specified in patent claim 11. A production method for an apparatus according to the invention is specified in patent claim 13. Advantageous configurations of the invention are the subject-matter of the dependent claims.

The apparatus according to the invention for flow cytometry comprises a flow channel, a magnetic unit, which is arranged below the channel bottom of the flow channel and is configured in order to generate a gradient magnetic field which permeates the volume enclosed by the flow channel, at least one cell measuring device, and at least one guide step, which is arranged in the flow channel in such a way that cells that can flow through the flow channel can be deflected toward the cell measuring device by the guide step. This has the advantage that the cells to be detected in a microfluidic system can be enriched in two dimensions by the flow conditions and the gradient magnetic field. The apparatus furthermore has the advantage of being able to obviate magnetophoretic enrichment and therefore of being structurally much less elaborate than previously known enrichment sections.

In one advantageous embodiment of the invention, the apparatus comprises a flow channel which is configured with respect to channel diameter and surface condition of the inner wall of the channel in such a way that a flow of a complex cell suspension in the flow channel can be generated with a laminar flow profile. In particular, the flow channel is a microfluidic channel. Operation is preferably carried out with relatively large channel diameters, which ensure laminar flow of a complex solution without obstructions occurring, for example due to deposits. The configuration of the channel with the guide step furthermore ensures enrichment in the direction of the cell measuring device, which makes it possible to obviate a Y-shaped microfluidic system such as is used for example for the separation of marked cells in the prior art.

In another advantageous embodiment of the invention, the apparatus comprises a magnetic unit which is configured in order to generate a gradient magnetic field by which magnetically marked cells can be enriched on the channel bottom. The marking of the cells is, in particular, superparamagnetic marking, for example by means of superparamagnetic beads. This has the advantage that all magnetically marked cells can be enriched on the channel bottom, where they are brought in the laminar flow to the at least one guide step, so that they can be deflected by the latter. In this case, the guide step has a height of about the cell diameter of the cell type to be detected.

The guide step in the apparatus is, in particular, an elevation relative to the channel bottom or is formed from a depression relative to the channel bottom. That is to say, the guide step forms for example a narrowing of the channel by extending as an elevation into the channel volume, or it forms a widening of the channel by being formed as the edge of a depression, so to speak a trough, in the channel bottom. By virtue of these guide step embodiments, different fluid-mechanical influences can be exerted on the cell sample.

In the case of elevations relative to the channel bottom, the step height is the height of the elevation, and in the case of a depression relative to the channel bottom the step height is so to speak the depth of the trough in the channel bottom. In this case, the trough outer wall, onto which the flow runs, so to speak forms the guide step.

In particular, the apparatus comprises a multiplicity of guide steps. These are arranged in the flow channel in such a way that cells that can flow through the flow channel can be enriched by the guide steps in a subvolume of the flow channel over a subsurface of the channel bottom. This has the advantage that the apparatus does not involve a Y-shaped microfluidic system in which marked cells are sorted, but instead enrichment of the cells to be detected is possible within the sample volume. Expediently, the subvolume or the subsurface of the channel bottom lies in the middle of the flow channel, toward which the cells can be enriched from both sides. In particular, the cell measuring device is then also arranged within the subsurface of the channel bottom. The cell measuring device is, for example, arranged on or in the channel bottom. In particular, the detection region of the cell measuring device extends beyond the subvolume above the cell measuring device.

The elevations of the guide steps are, in particular, configured in such a way that the cells cannot become stuck in the intermediate spaces between the guide steps, and cannot obstruct these intermediate spaces. The structure height, that is to say the height of the steps relative to the channel bottom, is therefore preferably of the order of the cell diameter, preferably slightly less than the cell diameter. The arrangement of a plurality of guide steps must leave free a sufficiently large subregion of the channel bottom, on which the enriched cells can continue on their way through the flow channel. Either a sufficiently wide channel is kept free between the guide steps or, as an alternative, a sufficient offset is ensured in the case of finger structures.

In one exemplary embodiment of the apparatus, the guide steps may be formed by means of photoresist strips, for example on a silicon wafer. To this end, the photoresist steps are generated in particular by means of photolithography.

Advantageously, the enrichment section is formed as a unitary plastic part with the guide steps, in particular by means of injection molding, so that the enrichment section does not occupy any silicon substrate. This has the advantage of reducing the silicon footprint and therefore the production and component costs of the flow cytometry apparatus.

In one advantageous configuration of the invention, the guide steps of the apparatus extend over the channel bottom in such a way that magnetically marked cells, which experience a magnetic force in the direction of the channel bottom and a fluidic shear force in the flow direction, can cross the guide steps only on a path over a predeterminable subsurface of the channel bottom. That is to say, the guide steps meet in particular with the channel walls on both sides of the channel bottom in such a way that magnetically marked cells enriched on the channel bottom cannot flow along the channel walls. In particular, the guide steps extend over both longitudinal halves of the channel bottom, respectively from one channel wall approximately as far as the middle of the channel, where a passage for cells enriched on the channel bottom is ensured in the flow direction. In this case, the guide steps may, in particular, be arranged in such a way that the subsurface over which the marked cells are enriched is a narrow rectangular subsurface which extends along the middle of the channel in the flow direction. As an alternative, the guide steps may also engage in one another in the manner of fingers, so that the subsurface over which the cells are enriched represents a subsection extending in a zigzag or in the shape of a wave. In particular, the subsurface in the direction of which the cells are enriched may also taper in the course of the flow channel in the flow direction.

In one advantageous embodiment of the invention, the guide steps are configured integrally with the channel bottom. In particular, the guide steps may be configured with the channel bottom as an injection-molded part. The embodiment as an injection-molded part has the advantage that, for the cell measurement, the enrichment section does not additionally have to be arranged on the substrate, which is expediently a silicon wafer in most cases. In this way, the so-called footprint, that is to say the size of the silicon substrate, for the flow cytometry component can be reduced considerably, which also reduces the cost of such a flow cytometry apparatus. Furthermore, the configuration of the fluid-mechanical enrichment section is substantially simpler to produce, above all compared with lithographic methods such as are used, for example, in the production of magnetophoretic enrichment sections.

In particular, the guide steps are straight linear elevations relative to the channel bottom. With the straight linear shape, the cells enriched on the bottom are transported by the laminar flow along the steps, without perturbing turbulence occurring in the flow at the channel bottom. As an alternative, the guide steps may extend in a curve in the direction of the middle of the channel. For the orientation of the straight linear steps, these are in particular arranged at an acute angle with respect to the flow direction. That is to say that the enriched cells which are to be transported along the guide steps are not held back by the latter, but rather the transport of the cells continues in the flow direction.

Advantageously, the apparatus with the enrichment section comprises a combination of guide steps on a separate plastic channel segment, these being for example configured integrally with the channel bottom, and a small part of the enrichment section by means of photoresist steps on the silicon wafer, on which the cell measuring device is also arranged. By means of such a combination, the silicon footprint can be reduced. The cells are enriched on an enrichment section of any desired length by the geometry of the guide steps and the fluid-mechanical conditions and, as soon as they reach the silicon wafer, they are also enriched there before the cell measuring device, which is preferably also preceded by a few guide steps, in order to maintain the enrichment and alignment of the cells when passing over the new channel bottom substrate.

The hybrid form of the enrichment section thus forms an advantageous variant for reducing the silicon footprint. The structure of the fluid-mechanical enrichment section by means of the guide steps on a plastic substrate then, for example, precedes the silicon die. In particular, the magnetoresistive components for detection of the magnetically marked individual cells lie on the silicon die.

A hybrid enrichment section of this type may, for example, also comprise a part in which the guide steps contain a proportion of nickel, or are produced as nickel strips. With a proportion of nickel in the guide steps, excess unbound magnetic markers can be retained by magnetic holding forces on the nickel strips or nickel guide steps, and so to speak filtered out of the complex suspension. In particular, nickel guide steps are structured by means of laser ablation. In particular, the guide steps with a proportion of nickel precede the enrichment section with the guide steps not containing nickel, that is to say they are arranged before the guide steps in the flow direction in the channel. As an alternative, however, the guide and filter strips containing nickel may also be arranged on the silicon substrate immediately before reaching the cell measuring device, and fulfill there the double function of enrichment and guidance as well as filtering of excess markers.

The dynamic enrichment and cell guidance in the flow ensures the advantage of the apparatus that enrichment and measurement can be carried out in one channel. The apparatus is not intended for sorting by means of Y-shaped separation of marked cells from the surrounding complex suspension, and furthermore excess markers do not have to be separated elaborately from the suspension, but can be retained by the guide steps. In particular, the guide steps are arranged in terms of their height and their angle with respect to the flow direction in such a way that unbound magnetic markers, which are very much smaller in terms of their hydrodynamic diameter than marked cells, remain on the guide steps and are held back, i.e. they cannot cross the steps. Only the larger fractions or particles, such as marked cells in the complex suspension, are entrained in the laminar flow and are thus transported along the steps. That is to say nonmagnetic, or nonmagnetophoretic, enrichment as in this case, by means of the guide steps, can also exert a filter effect on excess and therefore undesired markers in the measurement region of the cell measuring device.

In order to reinforce the fluid-mechanical filter effect at the guide steps, which in particular are nonmagnetic, i.e. do not contain a proportion of nickel, these may be varied in terms of height, i.e. in particular adapted to the size of the cell type to be detected and the size of the unbound magnetic particles, or markers, to be filtered. In one advantageous embodiment, the step height increases in the course of the flow channel in the flow direction. The first step is still very low and can be crossed by most particles and cells. In the course of the channel, the step height then rises increasingly and thus retains larger and larger particles. Only the magnetically marked cells which are intended to be detected are not stopped by the steps, but are transported along the steps and concentrated in a subvolume of the channel. To this end, all steps point in particular toward this subvolume, which lies particularly in the middle of the channel on the channel bottom.

The channel diameter, or the channel height and width, are in particular a few hundred μm, for example 200 μm. The step height is dependent on the cell type to be detected and the cell diameter thereof, and is in particular a few micrometers, for example 10 μm or up to 30 μm. The flow channel may thus, in particular, guide a sufficiently large volume of a complex suspension without thereby being obstructed.

In the method according to the invention for magnetic flow cytometry, a laminar flow of a cell sample is generated and the cells are enriched by means of guide steps in a predeterminable subvolume of the flow channel. In this case, the cells to be detected are magnetically marked and are dynamically enriched on the channel bottom in a gradient magnetic field. This method has the advantage that fluid-mechanical and magnetic forces interact in such a way that magnetically marked cells can be enriched in a controlled manner in a predeterminable volume, without their needing to be separated from the cell suspension. In one advantageous embodiment of the method, the subvolume extends in the flow direction along the channel bottom, so that the cells are guided along an axis individually over a cell measuring device.

For the flow cytometry method, for example, a blood sample is transported in a laminar fashion through the microfluidic system. In the flow, the cells are partially aligned close to the channel bottom by the structuring of the substrate, i.e. the guide steps. In the gradient field, for example, superparamagnetic analytes are drawn onto the structured channel bottom and detected there magnetoresistively.

In the method according to the invention for magnetic flow cytometry, three forces thus act on the magnetically marked cells or on magnetic beads, or generally on magnetic particles to be detected: The magnetic force of the gradient magnetic field, which is generated by the magnetic unit below the channel bottom. Magnetic field strengths of this gradient field are, for example, between 1 and 300 mT. This magnetic force thus attracts the cells perpendicularly toward the channel bottom surface. Furthermore, the shear force of the flowing cell sample acts on the individual cells. The flow is, in particular, a laminar flow. This force thus acts in the direction of the cell sample flow through the channel. A third force is exerted by the guide steps on the channel bottom, which represent a fluid-mechanical obstacle for the magnetically marked cells enriched on the bottom. The effect of this is that, in order to proceed further in the flow direction, the cells move along the guide steps toward the middle of the channel or in general, depending on the orientation of the guide steps, toward a subregion of the channel. The magnetic marking is preferably carried out using superparamagnetic particles.

When the flow cytometry method is carried out, the flow rate, the surface property and the magnetic field strength also play a role. The flow rate, for instance, is adapted in particular to the cell sample and above all to the channel diameter, in order to ensure a laminar flow. By means of surface functionalization, the surface properties of the channel inner walls and of the channel bottom can be optimized. By means of the field strength of the gradient magnetic field, further influence can be exerted on the cells to be deflected and enriched. The cells to be detected also have mechanical properties, which can be influenced by the values of the flow rate, surface condition and magnetic field strength.

In the production method according to the invention for an apparatus for flow cytometry, guide steps are configured integrally with the channel bottom, particularly as an injection-molded part.

The apparatus according to the invention thus has the advantage of offering a solution for flow cytometry without magnetophoresis. For example, a substrate structured in this way, which correspondingly guides and enriches the magnetically marked cells by the guide steps, i.e. the structure of the substrate bottom, can be produced by various techniques, inter alia injection molding or embossing. Accordingly, no lithographic outlay such as in magnetophoretic enrichment is necessary. So to speak, the magnetic guide lines of a magnetophoretic enrichment section are replaced by a three-dimensional structure of the substrate bottom. In particular, the preferred herringbone shape is adopted in this case. The structuring has, in particular, linear elevations which are referred to as guide steps. These are arranged in particular at a steep angle to the flow direction through the channel. The steps typically measure heights of between 0.1 and 20 μm relative to the channel bottom. In their width, the guide steps measure between 1 and 100 μm, for example. The length of the guide steps is selected, as a function of the channel width, in such a way that they end at the channel edge with the channel wall, and reach approximately to the middle of the channel. Either they reach only almost as far as the middle, so that a passage remains between the guide steps which extend from both sides in the direction of the middle of the channel, or as an alternative they extend in terms of their length beyond the middle of the channel and are then arranged engaging in one another in the manner of fingers. The angle with respect to the flow direction is for example less than 45°, in particular less than 20°.

In the flow cytometry method, in particular, a blood sample is transported in a laminar fashion through the microfluidic system. Cells within this blood sample are partially aligned close to the substrate surface by the substrate structuring. Magnetically marked analytes, in particular superparamagnetically marked analytes, are attracted in the gradient field onto the substrate surface, i.e. onto the channel bottom, and are guided close to the substrate, i.e. on the channel bottom, where the substrate structuring can influence them. The cells enriched and aligned in this way can then be detected magnetoresistively.

Embodiments of the present invention will be described by way of example with reference to FIGS. 1 to 7 of the appended drawing:

FIG. 1 shows a perspective representation of the channel bottom with the cell-guiding elevations,

FIG. 2 shows a longitudinal section, or a side view, of the channel bottom with underlying permanent magnets,

FIG. 3 shows a cross section, or a front view, of the flow channel,

FIG. 4 shows a plan view of the arrangement with the guide troughs, or steps, arranged in a herringbone fashion,

FIG. 5 shows another plan view of the arrangement with the guide troughs, or steps, arranged in a herringbone fashion,

FIG. 6 shows an enlarged detail of FIG. 4, and

FIG. 7 shows a hybrid cell enrichment section.

FIG. 1 shows a perspective view of the channel bottom 13, which is represented as a flat substrate. At a distance thereunder, a further flat cuboid 20 is shown, which represents the magnetic unit 20. The magnetic unit is, in particular, a permanent magnet.

The magnetic unit 20 may also extend over an area larger than that of the channel bottom 13, in order to ensure a homogeneous magnetic field in the region of the flow channel 100. In particular, the magnetic unit 20 generates in the flow channel 100 a gradient field in which magnetic particles, for instance the magnetically marked cells 1 or unbound magnetic markers, are enriched in the negative z direction toward the channel bottom 13. The x, y and z directions are respectively indicated by small coordinate systems at the edge in the figures. In FIG. 1, a multiplicity of guide steps 12 which are represented as narrow cuboids are arranged on the channel bottom substrate 13. These elevations 12 meet, in particular, the edge of the channel bottom, or the channel walls 14. The channel walls 14 are not shown in the representation of FIG. 1. The guide steps 12 project into the middle of the channel, although they do not join there with the opposite guide steps but either leave a straight passage in the middle or engage in one another in the manner of fingers, in such a way that a zigzag or serpentine line can extend through the guide steps. Possible flow paths of magnetically marked cells 1 are indicated by arrows 41 in FIG. 1. The magnetically marked cells 1 are shown as circles or ovals. The forces 10 _(x,y,z) acting on the cells are indicated by double arrows. In turn, wide double arrows indicate the flow direction 40, which extends from left to right in FIG. 1. In the flow channel 100, the magnetically marked cells 1 are thus introduced at one end within a complex cell suspension and flow in the flow direction 40 through the enrichment section with the guide steps 12. Owing to the magnetic force 10 _(z), which points in the direction of the channel bottom 13, the shear force 10 of the liquid in laminar flow, which points in the flow direction 40, and owing to the guide steps 12 which represent a barrier, which in turn exert a mechanical force 10 _(x) in the x-y plane of FIG. 1 on the cells 1, the cells 1 are displaced along the guide steps in the direction of the subregion 130 of the channel bottom 13. At the end of this subregion 130, in which the cells 1 are concentrated, there is furthermore the cell measuring device 30 which, in particular, comprises at least one magnetoresistive element.

FIG. 2 shows a longitudinal section, or side view, of an apparatus similar to that in FIG. 1. In this case, two flat rectangles which represent the substrate, or the channel bottom 13, and at a distance thereunder the magnetic unit 20, are arranged above one another. As an alternative to the embodiment shown, the permanent magnet may also be arranged directly below the channel bottom 13 without a separation. Above the channel bottom 13, the flow direction 40, in FIG. 2 from left to right, is in turn indicated by a double arrow, and a cross section through three of the guide steps 12 as well as through the cell measuring device 30 at the right-hand end of FIG. 2, and therefore at the end of the enrichment section. Owing to the permanent magnet 20, the magnetically marked cells 1 experience a magnetic force 10 perpendicularly in the direction of the channel bottom 13. The height of the guide steps 12 is in particular adapted to the extent, i.e. the hydrodynamic diameter, of the magnetically marked cells 1, and is in particular slightly less than the cell diameter. With a height which is too low, however, the magnetically marked cells would not experience any guide force 10 due to the steps 12, but would be carried away over them in the laminar flow. With excessively high barriers 12, the magnetically marked cells 1 would no longer experience any shear force 10 _(y) due to the flow, and would remain behind the steps 12.

FIG. 3 shows a cross section, or the front view, of the flow channel 100. In FIG. 3, the magnetic unit 20 and, at a distance thereover, the substrate 13 for the channel bottom are in turn shown as narrow rectangles, the channel wall 14 which encloses a cuboid channel volume being arranged thereover. In the flow channel 100, the subvolume 110 in which the magnetically marked cells 1 are enriched is also represented by dashes.

FIG. 4 in turn shows a plan view of the channel bottom 13, on which the flow direction from left to right in FIG. 4 is again indicated by double arrows 40. Respectively at the side of the channel bottom 13, the channel walls 14 are represented in section by shading. A dashed line, which denotes the end of the magnetic region, respectively extends inside the channel walls 14. That is to say, the distance between the dashed lines 200 shows the width of the region permeated by the magnetic field. It is, in particular, wider than the flow channel 100. This ensures that the magnetic field in the channel volume is as homogeneous as possible. The region 200 permeated by the magnetic field is generated by the magnetic unit 20, which is arranged below the channel bottom 13, as can be seen in FIGS. 1 to 3. In the channel 100, guide steps 12 are in turn arranged at an angle δ with respect to the channel wall 14, so that the guide steps 12 point from the channel wall 14 in the direction of the middle of the channel in the flow direction 40. The magnetically marked cells 1, as indicated by the flow paths 41, can thus be deflected at the guide steps 12 in the direction of the subregion 130, which extends as far as or beyond the cell measuring device 30.

FIG. 5 shows a possible arrangement of guide steps 12, which are arranged at a very acute angle δ with respect to one another. The channel width 100 is again indicated. FIG. 6 shows an enlarged detail of FIG. 5 with guide steps 12, converging at an acute angle δ, which have a step thickness or width d and a distance D between the steps. The angle δ at which the steps 12 are arranged with respect to the flow direction 40 may, for example, be measured relative to the midline of the channel as shown in FIG. 6, or relative to the channel wall 14. Again, magnetically marked cells 1 are indicated as small circles in FIG. 6. It is illustrated here that a sufficiently wide flow path through between the steps 12 is ensured for the cells 1, so that they do not obstruct the guide step intermediate spaces.

Lastly, FIG. 7 shows another possible configuration of the apparatus, with a hybrid enrichment section. In the left-hand region of FIG. 7, the enrichment section is shown on a plastic substrate 13 with plastic guide steps 12, with which lead to the described fluid-mechanical enrichment of the cells 1. This is followed in the right-hand region of the drawing by the substrate 13 of the silicon chip 15, on which the cell measuring device 30 is arranged. This may, as shown in the example of FIG. 7, also have further guide steps 125 which, in particular, continue the enrichment section onto the subregion 130.

The flow direction 40 is again represented by a double arrow from left to right in the drawing. The magnetically marked cells 1 are represented as ovals, and their flow paths are denoted by arrows 41. In the example shown in FIG. 7, the guide steps 12, which meet the channel walls 14 on both sides, do not engage in one another in the manner of fingers, but leave a straight flow region open in the region of the middle of the channel which lies in the enrichment subregion 130. In order still to guide the cells 1 straight over the cell measurement region 30 after the enrichment section through the guide steps 12, the silicon chip 15 also has a small portion of an enrichment section with guide steps 125. These may, for example, also contain a proportion of nickel in the material of the guide steps 125 and therefore filter out still unbound markers by magnetic retaining forces before the cell measuring device 30. As an alternative, the guide steps 125 may be produced on the silicon chip 15, for instance by photoresist structures. Furthermore, FIG. 7 again shows by double arrows the deflecting force 10 _(x) which guides the cells 1 along the guide steps 12 to the middle, as well as the shear force 10 _(y), of the fluid flow, which points in the flow direction 40. 

1. An apparatus for flow cytometry, having a flow channel (100), having a magnetic unit (20), which is arranged below the channel bottom (13) of the flow channel (100) and is configured in order to generate a gradient magnetic field which permeates the volume enclosed by the flow channel (100), at least one cell measuring device (30), and at least one guide step (12), which is arranged in the flow channel (100) in such a way that cells (1) that can flow through the flow channel (100) can be deflected toward the cell measuring device (30) by the guide step (12).
 2. The apparatus as claimed in claim 1, wherein the flow channel (100) is configured with respect to channel diameter and surface condition of the inner wall of the channel in such a way that a flow of a complex cell suspension in the flow channel (100) can be generated with a laminar flow profile.
 3. The apparatus as claimed in claim 1 or 2, wherein the magnetic unit (20) is configured in order to generate a gradient magnetic field by which magnetically marked cells (1), in particular superparamagnetically marked cells (1), can be enriched on the channel bottom (13).
 4. The apparatus as claimed in one of the preceding claims, wherein the guide step (12) is an elevation relative to the channel bottom (13) or is formed from a depression relative to the channel bottom (13).
 5. The apparatus as claimed in one of the preceding claims, having a multiplicity of guide steps (12) which are arranged in the flow channel (100) in such a way that cells (1) that can flow through the flow channel (100) can be enriched by the guide steps (12) in a subvolume of the flow channel (100) over a subsurface (130) of the channel bottom (13).
 6. The apparatus as claimed in one of the preceding claims, wherein the cell measuring device (30) is arranged on or in the channel bottom (13).
 7. The apparatus as claimed in one of the preceding claims, wherein the guide steps (12) extend over the channel bottom in such a way that magnetically marked cells (1), which experience a magnetic force (10 _(z)) in the direction of the channel bottom (13) and a fluidic shear force (10 _(y)) in the flow direction (40), can cross the guide steps (12) only on a path over a predeterminable subsurface (130) of the channel bottom (13).
 8. The apparatus as claimed in one of the preceding claims, wherein the guide steps (12) are configured integrally with the channel bottom (13), particularly as an injection- molded part.
 9. The apparatus as claimed in one of the preceding claims, wherein the guide steps (12) are straight linear elevations relative to the channel bottom (13).
 10. The apparatus as claimed in one of claims 5 to 9, wherein the guide steps (12) are arranged at an acute angle with respect to the flow direction (40).
 11. A method for magnetic flow cytometry, wherein a laminar flow of a cell sample is generated, the cells (1) are magnetically marked and are dynamically enriched on the channel bottom (13) in a gradient magnetic field, and wherein the cells (1) are enriched in a predeterminable subvolume (110) of the flow channel (100) over a subsurface (130) of the channel bottom (13) by means of guide steps (12).
 12. The method as claimed in claim 11, wherein the subsurface (130) extends in the flow direction (40) along the channel bottom (13), so that the cells (1) are guided along an axis over a cell measuring device (30).
 13. A production method for an apparatus as claimed in one of claims 1 to 10, wherein the guide steps (12) are configured integrally with the channel bottom (13), particularly as an injection-molded part. 